This invention relates to blood filters, and more particularly to filters designed to be implanted in a human vena cava and the like.
Vena cava filters are designed to capture emboli and prevent them from migrating via the blood stream into the pulmonary arteries. A vena cava filter is typically placed via a catheter inserted through a puncture in a vein. For insertion, the filter is collapsed within the catheter and is released after the catheter has accessed the vena cava.
Known vena cava filters in collapsed form have required relatively large diameter catheters and correspondingly large puncture openings which has limited the access point generally to the largest veins, i.e. the femoral and jugular veins. The relatively large puncture wound has at times produced complications.
The present invention provides filters of small collapsed construction that are self-centering in the human vena cava over the considerable range of diameters of vena cava that exist. The invention also provides a high degree of consistency and repeatability in placement of the filter and secure anchoring of the filter to the vein wall to ensure no movement, particularly during the acute phase, until tissue growth over the anchors occurs to make the filter more secure.
The invention has various aspects which individually contribute improvement, and which, in select combinations, enable a smaller collapsed form and improved performance to be achieved.
Specifically, in one important respect, a vena cava filter is provided which, by separation of the filtering and anchoring functions into two or more sets of legs or struts, enables small diameter collapse of each set, in a construction which is desirably short and in which the axially spaced wall contact of the sets achieves self-centering over a wide range of vena cava sizes. Secure anchoring is also achieved at a precise location against movement in either direction as a result of firm engagement of the anchoring devices.
According to one principle of the invention a set of filter-wires is provided, which is to achieve the clot capturing function, capable of deploying over a wide range of cone angles dependent upon the size of the vena cava. These filter-wires extend generally upstream from a central region of connection, to wall-engaging free ends. The filter-wires of the set desirably have a general helical matching configuration that presents an effective clot-capturing aspect, in a construction that is readily collapsible into a small compass. From the axis also extends a collapsible strut structure which supports wall-engaging anchors or projections that securely engage the vessel wall at a location or locations spaced axially from the region of contact of the free ends of the filter-wires. Because nearly all of the filtering action is accomplished by the set of helical filter-wires, the design of the strut structure need not deal with its filtering aspect. While other cross-sections are operable in certain circumstances, the struts are preferably of rectangular transverse cross-section, i.e. of strip form, the long dimension of this cross-section arranged circumferentially, and the struts extend at, effectively, a steeper angle relative to the longitudinal axis than do filter-wires. This steepness favorably affects their force-applying capability at the vena cava wall. Other strut cross-sections including oval and even circular can, however, be employed under certain circumstances.
The strut structures in certain preferred embodiments diverge to their wall-contacting points in the opposite axial direction to that of the filter-wires in order to achieve the self-centering effect. Because of the strip-form construction they can readily support multiple anchors or projections along their respective lengths in the outer regions to provide firm anchoring capability in both small and large vena cava. In another preferred form, the strut structure extends in the same axial direction as does the filter wire structure, but at a steeper effective angle to achieve firm anchoring at a location spaced axially from the wall contact region of the filter-wires. Again this structure achieves a secure self-centering function over a wide range of vena cava sizes. The self-centering performance of preferred embodiments is assisted by employment of linear axially parallel wall-engaging elements supported by the strut structure. These are particularly beneficial in embodiments in which the strut structure diverges in the same direction as the filter-wires, but also have applications in a xe2x80x9cski-likexe2x80x9d single support point configuration in which the strut structure diverges in the opposite direction from that of the set of filter-wires.
A parallelogram-like strut support of opposite ends of linear wall-engaging elements is an important feature in certain preferred embodiments. It enables the linear wall elements to maintain their parallel relationship to the axis of the filter, thus centering the filter over a range of sizes. This novel parallelogram support, while contributing significantly to the performance capability in combination with one of more sets of helical filter-wires, also has merit in its own right in which the support struts are constructed and arranged themselves to have a filtering function, or in which such strut structure is combined with other filtering arrays.
While presently preferred to be constructed of elastic metals such as nickel titanium alloy operating in the linear portion of the stress/strain curve, other materials can be used to advantage. Other materials of metallic or polymeric nature, including super-elastic metal, shape memory metal, and newly developing materials, may be used to advantage. Surface treatments of the filter-wires and supports can contribute to their effectiveness. Following the concepts provided herein, it becomes possible to form vena cava filters sufficiently small that in certain cases they may be introduced less invasively through smaller veins when access to the femoral or jugular vein is not possible.
These and other objects and features of the invention will be understood from the following summary of certain specific features of the invention and from the detailed description of presently preferred embodiments in connection with the drawings.
According to one aspect of the invention, there is provided a vascular filter for placement in a blood vessel for preventing the movement of emboli in the blood stream of a human. The filter includes a set of filter-wires that diverge from a central region in a given direction along the blood vessel forming an emboli-capturing array, the filter-wires having portions that engage the vessel wall, and an anchoring assembly defined by at least one set of struts joined centrally with said set of filter-wires. Portions of the anchoring assembly are constructed and arranged to engage the wall of the blood vessel in a manner anchoring the filter in position, the region of the anchoring being spaced from the region of contact of the set of filter wires with said vessel wall.
In preferred embodiments, the anchoring assembly includes anchoring formations supported by the struts and disposed for engagement with the walls of the blood vessel, each of the formations comprising at least one pointed projection to engage wall tissue and anchor the strut thereto.
In certain preferred embodiments each anchoring formation comprises at least a pair of pointed projections, the projections of the pair being oriented in opposite directions along the blood vessel, each being angled to penetrate wall tissue, the pair being effective in resisting dislodgement of the strut in either direction along the vessel. Also, in preferred embodiments the wall-engaging formations supported by the struts are constructed and arranged to maintain generally linear contact with the vessel walls.
In preferred embodiments of this aspect of the invention the filter-wires of the set are helically configured and arranged to form an effective clot-capturing array that can be radially expanded and contracted to adapt to vessels of different sizes.
According to another aspect of the invention, there is provided a vascular filter for placement in blood vessels for preventing the movement of emboli in the blood stream of a human, the filter comprising an emboli-capturing portion having a set of filter-wires joined at a central region and extending in a given direction along the blood vessel, and terminating in free ends constructed to engage the wall of the vessel, the wires having a diverging relationship to the axis of the filter. The filter features at least a major mid-portion of the length of the free ended wires of the set being of generally helical form, cooperatively related to form an effective emboli-capturing array.
Preferred embodiments of these aspects of the invention have one or more of the following features.
The filter-wires have substantially less transverse cross-section and are collapsible into a small size bundle. The filter wires are comprised of elastic metal of round cross-section, their helical extent being curved at a radius of the order of xc2xc inch to xc2xd inch and the struts are comprised of flat strip-form material arranged with the direction of thickness of the strip oriented radially.
The filter wires are comprised of elastic material, the wires being cooperatively related, upon compaction, to elastically straighten and to meet closely with each other, enabling into a small size, and enabling radial compaction of the set into an introducer catheter of about 9 French or less outer diameter for insertion into a blood vessel. The wires when released from the catheter into the blood vessel are constructed to expand to form the effective emboli-capturing array.
The filter is constructed for placement in blood vessels over a range of sizes, portions of the filter-wires adjacent the free ends being relatively straight, enabling, substantially end-contact of the wires with the walls of the blood vessel over the range of vessel sizes.
Preferably, all of the filter-wires are curved in the same general helical direction. Alternatively, the wires of the set of filter-wires may comprise multiple subsets, the wires of one set being curved in the opposite helical direction from the helical direction of curvature of wires of another subset.
For anchoring the filter, an anchoring assembly provides anchoring formations distributed about the filter. The anchoring formations are provided with parallelogram-like supports arranged to adapt to the walls of vessels over a range of sizes while maintaining substantially the same attitude with respect to the walls of the vessel. Preferably the parallelogram-like supports are constructed and arranged to expand from a collapsed condition without change in the overall length of the filter.
In certain preferred embodiments of above mentioned aspects of the invention the struts diverge from the central region in a direction opposite to the direction of divergence of the filter-wires, the struts terminating in portions that engage the wall of the blood vessel, with the spacing of the regions of contact of the filter-wires and struts with the vascular wall being selected to stabilize the filter in the vessel in a generally centered relationship. In such embodiments, preferably the wall-engaging formations supported by the struts are constructed and arranged to maintain generally linear contact with the vessel walls, preferably the wall-engaging formations being linear elements each supported in its mid-region by a strut of the set.
In other preferred embodiments, the struts are short relative to the filter-wires and diverge in the same direction as the filter-wires, but at a greater angle relative to the longitudinal axis of the filter. The spacing of the regions of contact of the filter-wires and struts with the vascular wall are selected to stabilize the filter in the vessel in a generally centered relationship.
In such embodiments, preferably the outer, wall-engaging formations supported by the struts are constructed and arranged to maintain generally linear contact with the vessel walls, the wall-engaging formations being linear elements each supported in its mid-region by a strut of the set.
In preferred embodiments, wall-engaging formations are linear elements, the linear elements being supported at one end by a strut of the set, and the other end of each of the linear elements is joined to and supported by a respective strut of a second set of struts of the assembly, each of the linear elements comprising an integral extension of at least one of the respective supporting struts. Preferably, the struts of the second set are centrally joined to each other at a location spaced axially from the region at which the struts of first set are joined, providing effectively parallelogram-like support to the linear wall-engaging elements to assure substantially linear contact with the vessel wall over a range of sizes of the vessel.
In other preferred embodiments, the struts have free end portions constructed to engage the wall of the vessel, there being a plurality of anchoring formations on the strut. The formations are arranged so that one formation is relatively more effective for anchoring in walls of blood vessels of relatively large size and the other formation is relatively more effective for anchoring in walls of smaller size vessels.
Preferably, the anchoring formations comprise at least one pointed projection. In certain preferred embodiments, each anchoring formation comprises at least a pair of pointed projections, the projections of the pair being oriented in opposite directions along the blood vessel, each being angled to penetrate wall tissue and effective in resisting dislodgement of the strut in either direction along the vessel.
In certain embodiments, preferably the filter wires are of round cross-section and the struts are of rectangular transverse cross-section, the thin dimension of the strut cross-section being arranged in the radial direction.
In certain embodiments, preferably a surface treatment is included on the struts and/or wires that enhances their effectiveness. In certain embodiments the treatment is a biocompatible polymeric coating and in other embodiments it is a metal coating.
In one particular aspect of the invention there is provided a vascular filter for placement in blood vessels for preventing the movement of emboli in the blood stream of a human, the filter including an anchoring assembly comprising anchoring formations distributed about the filter and mounted on parallelogram-like supports arranged to adapt to the walls of vessels over a range of sizes.
Preferred embodiments of this aspect of the invention may have the following features.
The parallelogram supports themselves form at least part of an emboli-capturing array. The outer wall-engaging elements are constructed and arranged to make generally linear contact with the vessel wall, one end of each of the wall-engaging elements being joined to and supported by a strut of a first set of struts, and the other end of each of the wall-engaging elements being joined to and supported by a respective strut of a second set of struts. The second set of struts are centrally joined to each other at a location spaced axially from the region at which the first set of struts are joined, providing effectively parallelogram-like support to the outer, linear wall-engaging elements. Preferably each of the linear wall-engaging elements comprises an integral extension of at least one on the respective supporting struts.